A lot of what Col. Cooper opined on way back when has turned out to be less than perfect in practice. Let's face it - the 1911 has not turned out to be ideal SD handgun, despite Cooper's bromance with it.
Today, you can make a good argument that the 1911 is not the ideal SD handgun (although I know you would still get some who would disagree), but back in the 70s? Before the renaissance in semiauto pistols in the 80s, you had the 1911, the Hi-Power, and... not much else as far as semiauto combat pistols. The general consensus back then (not just Cooper) was that the 1911 was indeed the best choice as a SD handgun.
His notion that a bolt action rifle is the best answer to all known problems a single person on foot might encounter probably is not so. These days there are plenty of semi-auto designs that can do everything a bolt gun can do and more, and with roughly the same weight.
I don't think the scout rifle was ever held as the "best answer" to any need, but the idea was it was an
adequate answer to a
wide variety of needs. Even back then, there were better hunting rifles, better combat rifles, better sniper rifles, better target rifles. If you had a
specific usage in mind, the scout rifle was not the best choice.
Also, you need to realize that Cooper was part of the WWII generation and during WWII the bolt-action rifle was still for the most part the standard infantry combat weapon. The US was unusual in issuing the semiauto Garand to infantry. Germans, British, Soviets, etc. all used bolt actions through most of the war, so the idea of a bolt action rifle for possible fighting use was not as far fetched as it may appear today.
It seems to me his idea focused around the idea of some loner wondering around on the Great Plains or Rocky Mountains shooting an occasional elk or buffalo to eat now and then. What is the chance of that ever happening for anyone? It's no more logical than the bizarre "bug out" ideas some people claim to have that will just get them killed if they ever tried it.
Yes, the whole thing was probably a bit of a fantasy even in Coopers time, but people who build tricked out ARs or "combat" shotguns are following the same path today.